If the inside height of a window is not changed and if the window is moved or its border is changed, then the contents of the window are not lost but move with the window. Changing the inside width or height of the window causes its contents to be moved or lost (depending on the bit-gravity of the window) and causes children to be reconfigured (depending on their win-gravity). For a change of width and height, the (x, y) pairs are defined:
When a window with one of these bit-gravity values is resized, the corresponding pair defines the change in position of each pixel in the window. When a window with one of these win-gravities has its parent window resized, the corresponding pair defines the change in position of the window within the parent. When a window is so repositioned, a GravityNotify event is generated.
A bit-gravity of StaticGravity indicates that the contents or origin should not move relative to the origin of the root window. If the change in size of the window is coupled with a change in position (x, y), then for bit-gravity the change in position of each pixel is (-x, -y), and for win-gravity the change in position of a child when its parent is so resized is (-x, -y). Note that StaticGravity still only takes effect when the width or height of the window is changed, not when the window is moved.
A bit-gravity of ForgetGravity indicates that the window's contents are always discarded after a size change, even if a backing store or save under has been requested. The window is tiled with its background and zero or more Expose events are generated. If no background is defined, the existing screen contents are not altered. Some X servers may also ignore the specified bit-gravity and always generate Expose events.
The contents and borders of inferiors are not affected by their parent's bit-gravity. A server is permitted to ignore the specified bit-gravity and use Forget instead.
A win-gravity of UnmapGravity is like NorthWestGravity (the window is not moved), except the child is also unmapped when the parent is resized, and an UnmapNotify event is generated.